Among the known front vehicle body structures are ones having left and right front side members (hereinafter referred to as “vehicle body frames”) made of a light alloy material, such as aluminum alloy, as disclosed, for example, in Japanese Patent Application Laid-Open Publication Nos. HEI-11-208519 (JP-A-11-208519) and 2003-72587 (JP-A-2003-72587).
Each of the vehicle body frames disclosed in JP-A-11-208519 and JP-A-2003-72587 is a hollow, tubular structure which has an outer wall formed into a regular polygonal shape (e.g., regular hexagonal shape) and a plurality of radial ribs connecting between the individual apexes and the central axis of the outer wall. With each of these disclosed vehicle body frames, which is made of a light alloy material, such as aluminum alloy, it is possible to properly stand or bear a compressive stress produced when an impact has occurred in the axial direction of the vehicle body frame. The left and right vehicle body frames are component parts that define engine room frames. The engine is disposed between the left and right vehicle body frames, and left and right front wheels are disposed outwardly of the left and right vehicle body frames.
Some of the known vehicle body frames have bent portions formed in correspondence with a layout of the engine (transversely-mounted engine) and front road wheel. With such a vehicle body frame having bent portions, however, it is difficult to secure a sufficient energy absorption amount when an impact has been applied to a front portion of the vehicle body frame. Thus, it has been conventional to achieve a sufficient energy absorption amount, such as by increasing the thickness of the vehicle body frame.
Therefore, there has been a great need to put into practical use a technique which allows a sufficient energy absorption amount to be secured without increasing the thickness and hence the weight of a vehicle body frame having a bent portion.